This invention generally relates to power supplies. More particularly, this invention relates to self-contained mobile power supplies for providing DC power to welding equipment and, simultaneously, AC power to conventional AC-powered tools.
Typical arc welding applications consist of a high current capacity electrode at a predetermined DC potential and a high current capacity electrode at ground potential electrically coupled to a metallic workpiece. As the non-zero potential electrode is moved towards the workpiece, a free-space current stream, or arc, develops, wherein sufficient heat is generated to melt the metal and create a weld. Due to the high current requirements of DC welding, DC welding power supplies are traditionally bulky and not easily transported.
Arc welding power supplies generally fall within three categoriesxe2x80x94power is derived from an AC power grid power, power is derived from a gasoline generator or power is derived from an internal DC source such as storage batteries. Arc welding power sources that derive DC welding power from an AC grid power, such as generated by public utility companies, can be made small and mobile, but must always be located near an AC outlet or tap. Thus, such power supplies may not be utilized in remote locations where AC power is unavailable. Arc welding power supplies that derive power from a gasoline driven generator can be located where AC power is unavailable, but typically are heavy, are noisy, require a supply of gasoline and pollute the atmosphere. Power supplies that derive welding current from internal storage batteries are self-contained, but are not equipped to provide power to AC tools such as grinders, circular saws, drills, etc.
Several portable electric power supplies wherein the primary power is taken from one or more DC storage batteries are known in the prior art. For example, U.S. Pat. No. 6,225,596 to Chandler, et al., discloses a portable welding unit comprising a housing containing a pair of series connected batteries therein. The welding unit has a ground clamp and cable connected to the positive terminal of the first battery and a welding gun and cable electrically connected to the negative terminal of the second battery. The unit also encloses a wire feed mechanism for feeding wire through the welding gun from a spool rotatably connected to the housing. Whereas the system of Chandler provides a compact self-contained DC welding power supply, there is no provision for operating AC power tools therefrom.
U.S. Pat. No. 3,694,729 to Jones discloses a portable electric power device in which a battery pack is housed to provide power for DC-operated tools. As is the case with the portable welding unit of Chandler, et al., the power supply of Jones does not incorporate means for operating AC power equipment.
U.S. Pat. No. 4,376,250 to Baker, Jr., et al., is directed to a portable power source providing alternating power for power devices derived from a plurality of DC storage batteries, or the like. The system includes a power inverter for transforming DC power into usable AC output power and a battery charger from which external AC power is converted into DC power with which the storage batteries are recharged. The system does not provide means for supplying a large quantity of DC current to a DC-operated tool such as a welder. Further, since the primary DC current is inverted to form an alternating current, diverting the majority of DC current to operate a welder would seriously effect the supply""s ability to provide sufficient AC power.
U.S. Pat. No. 5,410,126 to Miller, et al., discloses a portable AC/DC wire feed welder which includes a mechanism to receive either AC or DC power and a selector mechanism to selectively activate the external DC source mode, an external AC source mode, and an internal AC source mode. The housing of the welding unit is fitted with an AC outlet for providing power to AC tools, however, AC power thereat is available only when an external AC power source is coupled thereto.
As can be drawn from the limitations of devices representing the prior art, there exists a need for a DC arc welding power supply for use in remote locations that is lightweight, compact, self-contained, and does not require flammable fuel. Moreover, the power supply should include an AC power source capable of driving conventional AC power tools.
An integrated mobile tool and welder power supply system of the present invention includes a primary DC power source coupled to a DC output terminal for supplying DC power to a DC-operated tool such as a welder, and further coupled to a power inverter for converting DC power to an inverted AC power signal for supplying AC power to AC-operated power tools. The integrated mobile tool and welder power supply system includes an AC power detector for detecting an external AC power signal such that when external AC power is available, AC-operated power tools may be operated by power from the external AC source rather than the power inverter. The integrated mobile tool and welder power supply further includes at least one power converter for converting an AC power signal or a DC power signal to a DC power signal for replenishing the primary DC power source to an optimal power level.
In another embodiment of the present invention, the integrated mobile tool and welder power supply includes a DC transfer switch coupled to a DC-DC power converter, a DC motor supply terminal, a motor demand indicator terminal, and the primary DC power source for supplying regulated power to a DC motor such as the welding wire spool motor found on some portable welders. When it is determined via the motor demand indicator terminal that the DC motor requires DC power, the transfer switch configures a current path, wherein motor power is taken from the output terminal of the DC-DC power converter and the DC-DC power converter takes at its input terminal DC power from the primary DC power source. This configuration of the invention allows the spool motor of a portable DC welder to operate independently of the primary DC power source so as to maintain a constant speed regardless of the load on the primary DC power source.